Testing of integrated circuits contained within ball grid array (BGA) packaging is accomplished through the use of what is commonly referred to in the art as a test socket. BGA test sockets typically include a housing mounted to a load board which interfaces with the test electronics. The load board is generally a circuit board for transferring test signals from the integrated circuit in the BGA to the test electronics.
Previous methods of attaching the test socket to the load board include through hole techniques and surface mounting techniques. In the surface mounting connection, the test socket includes test pads which make contact with the solder balls on the bottom of the BGA as the BGA is compressed against the test pads to transfer the test signals to the load board. A problem associated with the surface mounting test socket arrangement is that the solder balls on the bottom of the BGA can vary in height and good electrical contact between each solder ball and the test pad cannot always be assured. A second problem associated with surface mounting is that once the test pads become contaminated from the solder balls, the entire socket assembly must be replaced.
Through hole techniques for connecting the socket to the load board include holes drilled through the load board for the passage of spring loaded contact pins which contact the solder balls on the BGA and transfer the test signals to the load board through the contact between the test pins and the holes in the load board. A problem associated with the through hole socket arrangement is that the test pins extending up through the load board could easily be bent or damaged which would negatively impact the test results. To avoid this problem, a receptacle can be positioned between the socket and the load board to protect the test pins extending through the load board. The result of incorporating a receptacle requires the length of the test pins in the socket to be increased which creates a problem for testing high speed integrated circuits. To address this problem spring probes have been incorporated which have a short travel length, however with short travel springs, the spring life is short requiring constant replacement. In addition, the use of spring probes in the socket can create an impedance problem for the transfer of the test signal from the BGA to the load board.
Consequently, a need exists for a new test socket for BGA packages which reduces the problems associated with prior art test sockets.